1. Field of the Invention
The invention relates to a liquid crystal alignment agent, a liquid crystal alignment film, and a liquid crystal display element. More particularly, the invention relates to a liquid crystal alignment agent capable of forming a liquid crystal alignment film having good ultraviolet reliability, a liquid crystal alignment film formed by the liquid crystal alignment agent, and a liquid crystal display element having the liquid crystal alignment film.
2. Description of Related Art
In recent years, due to the gradual increase in the consumer demand for wide viewing angle characteristics of the liquid crystal display, the demand for electrical characteristics or display characteristics of the wide viewing angle liquid crystal display element is higher. Among wide viewing angle liquid crystal display elements, the vertical alignment liquid crystal display element is the most commonly studied. Therefore, to have better electrical characteristics and display characteristics, the liquid crystal alignment film has become one of the important objects of study for improving the characteristics of the vertical alignment liquid crystal display element. In particular, after the large-size LCD TV has been put into extensive use, maintaining the reliability of prolonged use has become more important for the large-size LCD TV in comparison to a display that mainly displays characters or still pictures.
Japanese Unexamined Patent Publication No. 9-176651 discloses a liquid crystal alignment film having high pretilt angle. By using a tetracarboxylic dianhydride compound having a steroid skeleton and a diamine compound having a steroid skeleton in the liquid crystal alignment film at the same time, high pretilt angle of the liquid crystal alignment film can still be maintained after a reliability test. However, the liquid crystal alignment film has the issue of poor ultraviolet reliability. Specifically, after the liquid crystal alignment film is irradiated by ultraviolet for a period of time, the situation of significantly reduced voltage holding ratio of the liquid crystal display occurs, thereby causing issues such as reduced contrast of the liquid crystal display.
Therefore, how to provide a liquid crystal alignment agent capable of forming a liquid crystal alignment film having good ultraviolet reliability used in a liquid crystal display element such that high voltage holding ratio is still maintained after prolonged ultraviolet irradiation is a current issue those skilled in the art urgently need to solve.